This invention relates to the field of integrated circuit fabrication. More particularly, this invention relates to a planarized semiconductor on insulator structure that has a reduced number and severity of crystal dislocations.
Semiconductor on insulator is a technology that is used to enhance the performance of integrated circuits. The technology involves forming a relatively thin layer of a semiconducting material, such as silicon, over a layer of an insulating material, such as an oxide or nitride of the semiconducting material, like silicon oxide. Semiconductor on insulator integrated circuits tend to operate more reliably at faster speeds and at lower powers than do bulk semiconductor devices. One reason for this performance enhancement is that semiconductor on insulator integrated circuits tend to have relatively lower junction capacitances.
One method of forming semiconductor on insulator integrated circuits is called separation by ion implantation of oxygen, which is commonly referred to as SIMOX. In this method, oxygen is implanted at a certain target depth beneath the surface of a semiconducting substrate, such as a silicon substrate. The implanted substrate is then thermally processed to stimulate a reaction between the semiconductor and the oxygen atoms, producing an oxide layer that acts as an electrically insulating layer below a relatively thin overlying layer of the semiconducting material.
There are often incentives for combining semiconductor on insulator structures in the same monolithic integrated circuit with bulk semiconductor structures. For example, a given integrated circuit may have need for both the relatively faster and lower power semiconductor on insulator structures and the higher power handling bulk semiconductor structures.
Unfortunately, SIMOX tends to best produce structures where the entire surface of a substrate has been processed. In other words, the insulation layer precursor material is implanted across the entire surface of the substrate, and the insulation layer is formed beneath all portions of the surface of the substrate.
What is needed therefore is a method for producing a semiconductor on insulator structure in the same monolithic integrated circuit with a bulk semiconductor structure.
The above and other needs are met by a method of forming a semiconductor on insulator structure in a monolithic semiconducting substrate with a bulk semiconductor structure. A first portion of a surface of the monolithic semiconducting substrate is recessed without effecting a second portion of the surface of the monolithic semiconducting substrate. An insulator precursor species is implanted beneath the surface of the recessed first portion of the monolithic semiconducting substrate, and a trench is etched around the implanted and recessed first portion of the monolithic semiconducting substrate. The insulator precursor species is activated to form an insulator layer beneath the surface of the recessed first portion of the monolithic semiconducting substrate. The semiconductor on insulator structure is formed in the first portion of the monolithic semiconducting substrate, and the bulk semiconductor structure is formed in the second portion of the monolithic semiconducting substrate.
In this manner, both bulk structures and semiconductor on insulator structures are formed in the same monolithic substrate. By recessing the first portion prior to the activation and growth of the insulating layer, the surface of the first portion of the substrate is preferably substantially coplanar with the surface of the second portion of the substrate. Further, by also forming a trench around the implanted and recessed first portion of the substrate prior to the activation and growth of the insulating layer, the substrate tends to not suffer crystal dislocation damage as the insulating layer grows.
In various preferred embodiments of the invention the step of recessing the first portion of the surface of the substrate is accomplished by growing a thermal oxide layer on the surface of the substrate, and then depositing a nitride masking layer on the thermal oxide layer. A patterning layer is formed on the nitride masking layer, and openings are formed in the patterning layer. Portions of the nitride masking layer and the thermal oxide layer are etched through the openings in the patterning layer. The patterning layer is removed, and the first portion of the surface of the substrate underlying the etched portions of the nitride masking layer and thermal oxide layer are recessed. All material remaining on the surface of the substrate is stripped off.
In further preferred embodiments, the step of recessing the first portion of the surface of the substrate is accomplished by oxidizing the first portion of the surface of the substrate underlying the etched portions of the nitride masking layer and the thermal oxide layer to partially consume the substrate. Most preferably the oxidizing step forms an oxide layer of between about one hundred nanometers and about one thousand nanometers in thickness. In alternate embodiments the step of recessing the first portion of the surface of the substrate is accomplished by one or more of etching the first portion of the surface of the substrate with an etching solution or a dry etch.